1. Field of the Invention
This invention relates to a packaging structure having excellent moisture resistance and transparency and permits excellent withdrawal of goods packed therein, and to a process for production thereof.
This invention also pertains to a process for producing a composite sheet which can be suitably shaped into a packaging structure by vacuum forming and/or pressure forming.
2. Description of the Prior Art
Pharmaceuticals (in tablets, capsules, etc.), cosmetics and foodstuffs must be completely packed since insufficient packing can readily cause degeneration or spoilage. Furthermore, it is convenient if after packing these goods can be viewed from outside.
In order to meet such a requirement, there have previously been used packages obtained by filling such goods in accordance with vacuum forming and/or pressure forming using a single-layer sheet of polyvinyl chloride (PVC) or polypropylene (PP), or a composite sheet composed of a polyethylene (PE) sheet and PVC layers bonded to both surfaces of the polyethylene sheet by a dry laminating method.
Since a packaging structure formed of a single-layer sheet of PVC or PP has low moisture resistance, it is the usual practice to remedying this defect by putting the packaging structure further in an aluminum bag. But the moisture resistance of the packaging structure after opening the aluminum bag is a problem, and filling of the package into the aluminum bag makes the manufacturing process complex and adds to the cost of production.
A package formed by using a composite sheet composed of P and PVC has fairly satisfactory moisture resistance in practical use, but the ease of withdrawing the contents from the package is not entirely satisfactory. Some of new drugs recently developed require higher moisture-proof than before, and for packing such drugs, the moisture resistance of packaging structure composed of the aforesaid composite sheet is still desired to be improved.